//data patch
string[] tekst = File.ReadAllLines(@"C:\zoo.txt");
//full of array - you allready have a string[], no need for a new one
//string[] tablica = tekst;
for(int s=0;s<tekst.Length;s++)
{
Console.WriteLine(tekst[s]);
}
//----------------Show all of array---------------------------//
//----------------Giv a number of column-----------------////
// try to use names with some meaning for variables, for example instead of "a" use "column" for the column
Console.WriteLine("Podaj kolumne");
int column = Convert.ToInt32(Console.ReadLine());
// your result for zeros in a given column
int suma = 0;
// for each line in your string[]
foreach ( string line in tekst )
{
// get the line separated by comas
string[] lineColumns = line.Split(',');
// check if that column is a zero, remember index is base 0
if ( lineColumns[column-1] == "0" )
suma++;
}
Console.WriteLine(suma);

EDIT: Just make sure to validate that the column they ask for, really exist in your array, AND if you do not consider the first column as the one with the name, adjust this part